When etching and film formation are performed on a semiconductor wafer, normally single semiconductor-wafer production equipment, with excellent reaction control, is used. The semiconductor wafer is placed on the surface of a holder which is positioned within a reaction chamber, and may be left as is, or may be fixed in place mechanically, or may be chucked in place by electrostatic force by applying a voltage to an electrode embedded in the holder, or otherwise fixed to the holder.
The temperature of the semiconductor wafer held in this way is rigorously controlled, in order to maintain uniformity of the film formation rate and etch rate during CVD (chemical vapor deposition), plasma CVD or similar, or during etching, plasma etching or similar. In order to perform such rigorous temperature control, the holder is heated by a resistive heating element incorporated in the holder, so that the semiconductor wafer is heated to a prescribed temperature by heat transmitted from the surface thereof.
The holder is supported by a cylindrical member at a portion other than the surface for holding a material to be treated, and installed within the reaction chamber. Lead wires are connected to electrodes provided in a portion of the holder other than the surface for holding the material to be treated, to supply power from outside to a resistive heating element, RF electrode, electrostatic chucking circuit, or similar embedded in the holder. The holder is formed from a material endowed with heat resistance, insulating properties, and corrosion resistance, such as for example a ceramic material such as aluminum nitride or silicon nitride. The cylindrical member is formed from the above ceramic material endowed with heat resistance and corrosion resistance, or from a metal such as W or Mo, or such a metal with a corrosion-resistant covering applied.
In conventional semiconductor manufacturing apparatus as described above, halogen gas and other highly corrosive gases are used as reactive gases in CVD, etching and other processes, and so the electrodes and lead wires of resistive heating elements and similar are housed within the cylindrical member mounted on the holder, and the two ends are hermetically sealed to the holder and the reaction chamber, so as to protect the lead wires from contact with corrosive gas.
However, although the interior of the cylindrical member is isolated from the corrosive gas, it is exposed to air, which is an oxidizing atmosphere, and so oxidation of electrodes is unavoidable. For example, when the holder is heated to 600° C. to induce CVD reaction of the treated material, the electrodes mounted on the rear surface of the holder are also exposed to an oxidizing atmosphere at approximately 600° C., so that it has been necessary to apply an oxidation-resistant seal to the electrodes for protection.
In addition to heating the treated material, a portion of the heat generated by the holder escapes via the cylindrical member and is wasted, being lost through thermal transfer to the air filling the interior space from the surface of the cylindrical member. Further, because the space between the cylindrical member and the reaction chamber is hermetically sealed with an O-ring, and forced cooling to 200° C. or below is performed in order to protect this O-ring, heat is lost at this cooled portion. Consequently the temperature of the holder is greatly reduced at the portion at which the cylindrical member is mounted, so that it is difficult to maintain thermal uniformity over the entire holding surface, and moreover the consumed power which is lost to waste is substantial.
Further, whereas the holder is heated to a high temperature such as from 300° C. to 800° C., the end portion of the cylindrical member supporting the holder is forcibly cooled to 200° C. or lower, as explained above, so that thermal stresses arise due to temperature differences in the length direction of the cylindrical member. If thermal gradients become too large, cracking may occur in the cylindrical member, which is formed from brittle ceramic material; hence it has been necessary to make the length of the cylindrical member, for example, approximately 300 mm.
In the case of ceramic cylindrical members, which must be fabricated by molding and sintering and cannot be fabricated by melting and hardening as with metal materials, manufacturing yields drop sharply as the length is increased, and moreover it is extremely difficult to perform the operations to apply an oxidation-resistant seal to electrodes within a long cylindrical member, so that production yields are lowered and costs are increased as a result. Further, because a holder with such a long cylindrical member mounted must be housed inside the reaction chamber, it is different to reduce the size of the reaction chamber.
The above problems with the prior art are not limited to a semiconductor manufacturing apparatus alone; similar problems arise in the case of a liquid crystal manufacturing apparatus in which a holder which holds a treated material and in which is embedded a resistive heating element must be held within an airtight reaction chamber.